Morfoanatomía del tallo con crecimiento secundario de especies de Jatropha (Euphorbiaceae) nativas de la Región Chaqueña Argentina y su relación con el ambiente

Abstract

Jatropha (Euphorbiaceae) is a morphologically diverse genus with pantropical distribution. It includes 180 species growing worldwide and has a broad range of uses: medicinal, ornamental and biodiesel production. In Argentina there are ten native species, distributed from the north to the center of the country, and one adventitious. However, the morphoanatomy of the native species of Jatropha is scarcely known, and so far, no anatomical studies of the stem with secondary growth have been performed in any of the native species. In this work, we analyzed the anatomy of the stem with secondary growth of three native species: J. excisa, J. hieronymi and J. macrocarpa, considering aspects related to the arid environment in which plants live, to provide information that it is useful for their conservation and possible sustainable use. Woody branches of each species were collected and fixed to perform temporary histological preparations of transverse and longitudinal sections of stems. We described their morphoanatomy under a light microscope. The following variables were analyzed: xylem area/total area of the stem, number of vessels per mm2, vessel diameter and length of conductive elements. Indices were obtained to assess the drought vulnerability, the plant mesomorphy degree and to determine vessel clustering. The stems analyzed have several anatomical characters that are typical of plants that inhabit xerophytic environments, and that favor their development despite the scarce rainfall and high temperatures, including: suber and phelodermis with thickened cell walls; inner cortex with various cell layers; presence of chollenchyma; presence of chlorenchyma; ergastic substances in the cortex, vascular tissues and medullary parenchyma (latex, crystals and starch granules); short, narrow, numerous and grouped xylem vessels. The evaluated indexes suggest that the three taxa have a safe and efficient conduction system for water movement, being J. macrocarpa the most drougth resistant. This study provides novel information about these three species of biological, industrial, and economic importance, which are potential sources for biodiesel production.